Syntheses, structures, and mesomorphism of a series of Ni(II) salen complexes with 4-substituted long alkoxy chains
A series of nickel(II) salen complexes containing 4-substituted alkoxy chains of aromatic rings, [Ni((4-CnH2n+1O)2salen)] (n=3 (1), 4 (2), 6 (3), 8 (4), 10 (5), 12 (6), 14 (7), 16 (8), 18 (9), and 20 (10)), and their parent complex, [Ni((4-HO)2salen)] (11) (salen=N,N′-ethylenebis(salicylideneiminato)), have been prepared and mesomorphic properties have been investigated. An X-ray crystallographic analysis revealed that complex 11·2DMF has one-dimensional stacking structure supported by the π–π interaction between the six-membered chelate and aromatic rings with the NiNi distances of alternatively 3.3957 and 3.7224Å and that complex 3 is formed by one-dimensional stacking by weak CH⋯O type hydrogen bonded interaction between the five-membered chelate ring and phenoxo atoms of the dramatically distorted salen moieties with the NiNi distance of 5.994Å. Complexes 1–6 did not exhibit any mesophases. On the other hand, complexes 7–10 with longer alkoxy chains of n=14–20 showed an unusual metallomesogen of a lamello-columnar mesophase within the smectic layers with an interlamellar distance of 31.1Å (7), 33.6Å (8), 37.1Å (9), and 39.5Å (10) and nearly constant stacking distance of 6.19–6.24Å between the inter-dimers, irrespective of the variation of the alkoxy chain lengths by the X-ray diffraction measurements of the liquid crystal. The relationship between molecular assemblies and mesomorphic properties is discussed.